Receiving apparatus for radiofrequency navigation systems



Nov. 2l, 1950 w. J. OBRIEN 2,530,902

RECEIVING APPARATUS EOR RADIO FREQUENCY NAVIGATION SYSTEMS Filed Aug. 27, 1945 2 Sheets-Sheet 1 IN1/EN TOR.

Arrone/V5 Ma/AMJ DB2/w Nov. 2l, 1950 w. J. o'BRxEN 2,530,902

` RECEIVING APPARATUS FOR RADIO FREQUENCY NAVIGATION SYSTEMS Filed Aug. 27, 1945 2 Sheets-Sheet 2 NNN satented Nov. 21., 19570 UNITED ySTATES PATENT( OFFICE RECEIVING A?*PARAA'liUSv F03' Rgiill)1`)j'V4 FREQUENCY N AVIGATIGBL SYSTEMS- William J GBrien, London, England, aisstgfncntgA The Decca Record Company, Limrrited;V Londonf England, a corporation of Great Britain' Application August 2'?, 1945, Serial-ibid. 612,99

5 fllatims.V (l. 33 105 My invention relatesV to radio frequency navi- -gationalV aidsv for determining and indicatingthe geographical location oi' a rnobilevelfiiole` andhasgpartioular reference to anovel forrnof` receiving appara-tus for use with naviga-tional systenlS ofk they multiplel equiphase, displacement type..

In my copending application Serial No. 612,987, filed. Aueuslti 2?. 19.45,, and.: entitled` Navigation: System,.now` abandoned,-` I have disclosed a radio frequency vnavigationalsystem whichpera-tes; to establish4 two intersecting coordinate. systems denedby;` contour-semanal phase `displacement between interferingradio.,frequency fields of unlike, but related:frequencies.V I have also disclosed; inmy copending` application Serial No. 6l2, 9 9l,v ledAugust 27, 1955; nov/#Patent No.V 2,500,200.. issued March i4, 1950, and; entitled Multiple ChannelRadio Frequency Receiver,V a reeeivingmapparatus whicnrnay be used'von the mobile vehicleY toreceive fthe transmissions irom the navigational equipment andi-provide` a continuous indication :of the; coordinate location of the vehicle. In4 the receiving apparatus4 describedrtherein, the separately receivedsignals are convertedto afrequency equal to the, least common multiple., of the twoY frequencies the relative phase,ofmwhichV it is ,desired :to: determine.

One possible objection to this rnode 0f operation lies in -the rather largeaniountof equipmentrequirccb tol eflectf` the.t necessary frequentieI ccnversieris; Also.v the. apparatus ldisclosed;is-inherf` ently,v cna; xed.; frecuemily;Y type which. once.v in:

stalled*lr isf. Suitable. for. use. only .on a single; set z ofA transmitting apparvatus.

Mvl first: aforementioned Copendingv; applica-f.. tion;` contemplates extendineathe Y Coverage; ofrtbei navigational, system ,over extremely large areas, by employing a plurality; ofgindividualsystenis oi;- the; type disclosed in thatv applicationrrand/ ranged;v tooverlap.y theirL respective;` usefuhV areas 1f ser as: to extend. the;v geographical coverage off. the system. The mobile receiven in ordertotaire;4 advantaeeloithe extendedrrange; and aecnnaevv of jsucha system; must be equipped withv receive.. ing4 means; whichr will permitL the prop er on@ orv the individual; nayigationalgsystemsitorbe selecte..` ed-outDfE the system network.

Because; onY the limitations above. noted., the.; present invention isv directed; to afvreoeiving:` ap: i p aratuswhich is; simpler, in.: constructionVY tiranv that; which` has` been.Y heretcfcre disclosed.Y andi whichk is, provided with` tuneableiV meanslv permite, ting a user of the system to select any one Ofiai.. grouper, navigationalgsystems forming; asLsyst-,em network.i

It is4v therefore; an; object of; my,v invention` to', providey ai. mobile; receivinaapparatus; for.;v use;A

with,navigational-system fof the character above; referred toandwhich operates ,to determine the relative vphase relations-,at a frequency-equal to a signal frequency,transmitted by the transmita. ting',apparatus.`

It is an additional object of my invention; to; provide. areceiving-apparatusrrof the character above referred to; which.; makes the;A phase com-v parisonat the lowest vsignalfrequency by hetero,- dyning the two received; frequencies oi` eachco, ordinate system, multiplying they heterodyne. frequencies to equality with the lowest signal. frequency, and comparing-the relative phase of the lowest signal frequency with eachV of ther multiplied heterodyne frequencies.v

It is also-theobjectA ofV my-inventionto pro-- vide inI an apparatusoithe character above re-V ferredtoia.means-.fordetermining the relativer phase VAdisplacement: between :two received Y signals orr thev basisofareference frequency equal to the leastfcommonemultiplef-of-the twosignal fre-- quencies.Y

It is a still further objectv of my invention to provide anapparatusv of' the nature above set for-th in which means-isprovided-for` tuning lthe receiving apparatusl tofallow-users of the system4 toY choose onev coordinate system out of a plurality of Such; systernsgproducedV by the op eration-of;` the navigational system network.

It isV an `additional, Vobjectoi` my inventionv to lprovide a receivingapparatus of the character set forth in the precedingparagraphs whichopf erates on-a heterodynefprincipal permittingv the use, of heterodynel frequency amplifiers whichv may be,soconstructed'asto provide a high gain andrexcellentv phase, stability. Y

OtherL objectssand; advantages of` my invention. will beA apparent from a study of the-following specication readfin connectionlwith the, accom,- panyingdrawines, wherein;

Fig. 1 isablock. diagramrillustrating the components employed and the manner of rtheir inter,-v connection to permit receiving .C radio frequency navigationalsigrlals. and. making a phase come parison betweedthe,receivedsignalsat a fre,- quency equal4 to... the lowestv transmitted` frequency;v and:

Fig. Zisablock diagramsimilar, to Fig.l 1 but o illustratinga 4tuneable receivingiapparatus which works into fixed heterodyne,Y frequency; ampliers arranged; to .make` the phase comparison atV frequencies ,10W-er, than. the lowesttransmittedfreqilenev- Referr-ing; to thev drawings, I havefiliustratedgin Fie. fbv dasrammatcal meansV the. apparatus; emnlovedzn one embodiment-yor; myy inventionvl toA provide. aY xedgfrequency. mobile. receiving. ap:-...

paratus suitable for use with a radio frequency navigational system of the character disclosed in my first aforementioned copending application. The equipment includes three radio frequency amplifiers I, 2 and 3 which are each coupled by suitable means to a receiving antenna lThe amplifiers I, 2 and 3 are tuned respectively to the three different but related frequencies transmitted by the navigational system and operating to establish the intersecting equiphase displacement coordinate system. For the purposes of illustration frequencies of 80, 60 and 90 kilocycles have been selected.

The operating frequencies of the various portions of the apparatus have been indicated in Fig. 1 by frequency notations enclosed in parenthesis. It will be appreciated that the specified frequencies are those corresponding to the assumed transmission frequencies of 80, 60 and 90 kilocycles and that other frequencies will be ernployed whenever the transmitting equipment is operated at frequencies other than those assumed.

The amplier I is coupled as indicated at 5 to one input of a mixer and detector circuit E, the other input thereof being coupled as indicated at 'I to the output of the amplifier 2. The mixing of the 80 and 50 kilocycle signals thus impressed upon the detector circuit 6 and the ensuing rectification of those signals results in a 2G kilocycle heterodyne frequency. This is amplified within the detector and amplier 6 and coupled as indicated at 8 to a frequence trebler and 60 kilocycle amplifier 9 operating to convert the 20 kilocycle input into a 69 kilocycle output. This output is coupled as indicated at Il) to one input of a phase discriminator circuit I I. The other input of the discriminator II is connected as indicated at I2 and I3 to the output of the amplifier 2 which also comprises a 60 kilocycle signal.

The phase discriminator I I operates to compare the phase relation between the 60 kilocycle signal received from the frequency trebler 9 and that received from the amplifier 2 and the result of this comparison is indicated as a phase angle by a phase angle indicator Id coupled as indicated at I5 to the output of the phase discriminator I I.

In a similar way the outputs of amplifiers 2 and 3 are coupled as indicated at I3 and Il to the input circuits of a detector and 30 kilocycle amplifler I8. The rectification of the two signals results in a heterodyne frequency of 30 kilocycles which is coupled as indicated at I9 to a frequency doubler and 60 kilocycle amplier 2i! operating to convert the 30 kilocycle input to a 60 kilocycle output. This output is coupled as indicated at 2l to one input of a second phase discriminator 22 the other input of which is connected as indicated at 23 and I3 to the output of a 60 kilocycle amplifier 2.

The phase discriminator 22 operates to measure the phase relation between the 60 kilocycle signal received from amplifier 2 and the 60 kilocycle converted frequency received from the doubler 2G. The result of this comparison is indicated as a phase angle on a phase angle indicator 2d coupled as indicated at 25 to the output of the phase discriminator 22.

With respect to the apparatus mentioned in the foregoing description, the amplifiers, detectors, frequency converters, phase discriminators and phase indicators may be of any suitable type. However, for the phase discrminators II and 22 a preference is expressed for the apparatus disclosed in my copending application Serial No.

612,991, filed August 2'7, 1945, and entitled Multiple Channel Radio Frequency Receiver, and for a phase indicator a preference is expressed for a goniometer of the character disclosed in my copending application Serial No. 612,984, led August 27, 1945, now Patent No. 2,499,326 issued February 28, 1950, and entitled Registering Goniometer.

Attention is directed to the fact that the phase discriminatoire II and 22 both make the required phase comparison at a frequency equal to the lowest frequency transmitted by the navigational system. It is also to be noted that the result of the phase determination which is indicated on the indicators I! and 213 is the relative phase 'oetween the two pair of navigational signals as measured on the basis of a reference frequency equal to the least common multiple of the respective transmitted frequencies. This may be explained as follows:

Assume that a phase of advancement of four degrees occurs in the kilocycle signal with no phase shift occurring in the 60 kilocycle signal as, for example, through movement of the mobile receiver in a circular path at a fixed distance from the 60 kilocycle transmitting antenna. The least common multiple reference frequency for the 60 and 80 kilocycle signals is 240 kilocycles or three times the 80 kilocycle signal. Therefore, the phase shift at the reference frequency of 240 kilocycles 'will be a phase advancement of twelve degrees or three times the actual advancement of the 80 kilocycle signal. The mixing of the 80 and 60 kilocycle signals in the detector circuit 6 produces an advancement of four degrees in the 2D kilocycle signal passed to the frequency trebler 9. The result of the frequency conversion is to advance the phase of the resulting 60 kilocycle signal three times as much as the advancement of the 2O kilocycle or a net advancement of twelve degrees. Therefore, the phase advancement of the 50 kilocycle signal applied to the phase discriminator II by means of the coupling I9 is twelve degrees, whereas no shift occurs in the signal coupled as indicated at I2 and 23. The indicated phase shift on the indicator I4 will accordingly be an advancement of twelve degrees.

Similarly if the phase of the 60 kilocycle signal received by the amplifier 2 advances three degrees while the phase of the kilocycle signal received by the amplifier 3 remains constant the indicated phase shift at the lowest common multiple frequency of kilocycles will be nine degrees. A three degree advancement of the phase of the 60 kilocycle signal results in a three degree retardation of the phase of the 30 kilocycle signal which is passed to4 the frequency doubler 2U. The frequency doubling effected by this circuit produces a phase retardation of six degrees in the 60 kilocycle output applied as indicated at 2l to one input of the phase discriminator 22. The other input of the phase discriminator 22 is coupled directly to the output of the amplifier 2 and the 60 kilocycle signal thus applied to the phase discriminator 22 is advanced three degrees. The net effect of the three degree advancement in one signal and a six degree retardation in the other produces an indicated phase shift of nine degrees in the advancing direction of the 60 kilocycle signal with respect to the 90 kilocycle signal.

In Fig. 2 I have disclosed a modied form of the invention directed particularly to a tuneable receiving apparatus permitting the use of the receiving equipmentwith different groups of radio frequency; Y transmitters serving.; as, indiani/tial2h navigational.- systemsf in. a. chain. or network: off.: suche, systems.. tratedin Fig.y 2 `includes variable frequency arn.V pliers;V 31,: 32;` and 33: the inputs. of` whha2r1ecolmectedL respectively throughy singlefpolef doublesthrow Switches 3.4, Beand; toasuitable.: receivingf antenna. 3l. As.` indire-.previously de-r scribed. modication of. the.- inventio-nity is.` as..-Y sumed that the transmitting;apparatus;v togwglnch;r the; equipment isftunecrV is. operated; respectively ais-80,60 and;.90;kilecycles.Al It;willeloeshown;sulpv sequently Vthat othenfrequencies may alsqbeused. providing; the; proper harmonic-.relation is maine tained..

Theoutputof the; amplifiers 31, 32,andf 33 are, respectively coupledI as;` indicated; .at- 38,; 379, and; Mrtcnniixing and detecting circuits f 4J 42, and43., Associated respectively with the amplifier/5,31,av 3-2; and 33; are variableA frequency amplifiers 4.4 4.5; and-.46; These ampliersaare. coupled'. to.: be exe. citedgv from a1 harmonic, generator 4 1 the output; of@ whchis coupled as.` indicated. at:y 48.*throush; arhigh passlter 49r having. a, lower cutoiefree q uency.:oftheordel1` o.f;magnitu.de of145 kilocycles. The high frequency I signals; passed. by. the. filter 4,9V areacoupled asindicatedat; 56,31. and 2;to the input circuits; respectively of the. ampliiers.k 4.111.',v t5 and 4.6.

The amplifiers, 45 and 46 are preferably of" f thezregenerative.type;designed to- .produce .an out-.-v But: Sig-nal; as closely. approaching a, sinusoidal. wave-formas. possible. If desired. the amplifiersV maygbe made regeneratiye to such an.r extentas. to beself-roscillating.. Thefoutputs off these amp lijels.: are respectively.- coupled. as. indicated. at 5354. and 5.5,to the input. circuits ofthe detectors 4t, 4.2 .and 43./within; whichlcircuits the signals oft different, frequency are IniXed. and rectified.; to;y produce output frequencies.7^ equal; to. the diner-rv ence-'between I the two input. frequencies.

In accordance with; the;r assumed.` example the;v harmonic generator preferably operates at a fundamental; frequency ofv i12/3... kilocycles'v with the.;amplifiersl 44, 4.5 andn 46 heineV tuned respec-` tively to; the eighth, sixth, and ninth, harmonics.- of the fundamental frequency of the harmonicL generator.; The amplifier 4.4;is,. therefore, tuned tm 9.31/3: kilocycles; the amplier 45Y is tuned te '711:-ki1ocyclesandthe amplifier-46 is tuned 'to-1051i kilocyclest As .a result the output frequencies'of the. detectors'r'i'l, 42 and 13t are respectivelySl/ k'locycles, llkilocyclesLand l-kilocycles.

TheV detectors are coupled as indicated` at 55;', 51: and 38V to Vheterodynefrequencyampliers 59; iandiBladjusted' respectively tooperate at-xed" frequencies of 131/3, 16 andl 15 kilocycles. The; 13d/fg kilocycle output of the heterodyne frequency amplifier 591s coupled as indicated at 5|. to an am-plier andfrequency treloler 62v operatingV to; produce a 4l) kilocyole. output signal which is applied as indicated'at 63 to one input circuit of a phase discriminator 64. The kilocycle Output of the heterodyne frequency amplifier 50 is divided as indicated at 65 and 66 and one half of the output is applied to the input ofa 10ki1`ocycle amplifierv and'ffrequency quadrupler 61 operatingvto convert the 10 kilocycle inputinto. a 4;.0` kilocycle output, which. output is appliedas indicatedat,68V t'o the other inputcircuit .of the phase; discriminator 54. Theo-utput of the phase discriminator 64 is coupled as indicated at 69 to a phase angle indicator 10 serving to indicate the relativefphase relation between the two 40kilo wel@ Snalsrapnled to;-.thefdiscrirninatoniik.

The apparatus which', is; illllSr.V

The` other; half.. of..V the 10,5 kilocyclei output: of; the.heterodyneffrequencyamplier 6u is applied asfindicated at66..-to.a' ldikilocycle amplifier and frequencyltrebler; Htoperating j to convert. the 10. kilocycleginput@ into,-a 30, kilocyvcle. output. This'. outputsisapplied-.asf.indicated; at '12.v to one. in.; put circuit of a 30 kilocycle phase discriminatori 13. The; 15, k-ilocycle output` ofthe heterodynel frequencyfamplier 6| is-rcoupledgasindicatedat 14: to.. al 15-l kfilocycle;w amplifier. and frequency doubler 'i5 serving to produce.- an output frequencyrfofi 3.0.kilocycles.;which is coupled asindicated at TB-to thefotherv input circuit. of the phase/discrimination 'i3- y The phase `discriminator operatestqmeasure:thesphase relation betweemthe4 two -30kilocycle input signals and to indicatefpyv meansof.` aphasefindicator 'i1 coupledl tothe discriminatori 13 as indicated. at 18 the. resultof the determination of the.- phase angle between .thetwo input signalsl.

As in the previously describedmodication of my invention and for` the-reasons. explained. in connection therewith the phase; indication given by. the indicatorsr'I-landr'l are. the phase relationshipslbetween the corresponding input signals as measured `on the basis-tof .reference frequency 1 equal to the least common multiple-of the two transmitted; frequencies.

In accordance .with the present modification oftheinvention thefampliers ill-33 and 44.-46 and the harmonic generator. 4:1. are vtunealole so that they;- may be used; to-se1ect transmissions fromfother-antennae at .frequenciesdiierent from thev8i),60,rand `99 kilocyclesignals iusedin the assumed example. To. simplify; the tuning` of the system` to other transmittersfV the tuningy controls forthe amplifiers andlharmonic generatorwill, by preference; be gangedgon apsingle control.

Assumingfthat the new; transmitters desired to loe received are operating-.on.8866 and. 99 kilocycles respectively, the. tuning control..` used. would .be advanced tostune-theampliers 31,; 32 and 33 respectively.. to these frequencies. At the saine time the frequency of theharmonic generator il would be raised.. toVv 122/3- lrilocycles.` The tuningc'nange. of. thefarnpliersf44, "i5Y and 46:Y wouldbeto resonance..withthe eighth, sixth andI ninth harmonics Aofthe12.*.2g-Vkil0cycle fundamental as-.beforef inpther.- words to frequencies of 101 1/3, 76'and1114kilocycles. Theeresulting heter-- odyne frequencies. are, therefore, unchanged, beingjrespectively. 131/3, loland 1 5.kilocycles.`

In `additionto .-thezforegingl *prefer to provide a means .for periodi,cally-1checkingithe` operation of the system tordetecttanyu spurious and unwanted` phase shiftswhichmay creep into the variouscircuits,I For this-reason Lemploy also a. referencefoscillator. 19. normally; operating on a 10 kilocycle fundamental. signal; to produce an output which is;- richfjnharmonicsso.. that by throwingv the switches;\'l.1,Y .35 and .36 to positions alternate ,to thosefshown;orrlFig.;.2 the output of.. the oscillator 'I9 may be Acoup;,ledglto the input 0117- cuitslcfthe-.amplifiersj, 32-and 33.550 that-.they may amplify the eighth;v` sixthand'ninth har.-r rnoncs l. respectively..- of., the` reference oscillators output, Thereferenceoscillatorfisfpreferably of a type which produces an output riclr;in.the. higher harmonics and in which the multiplefphase relation between vthese.' harmonics.4 1 isfxed and unchanging.. During. nal. testing; and; .adjust-.1 incr-1ty followingI construction,; the .various :circuit-z mnnponen-.ts:ly are.- preferablr; adiustedrtmfgiye a; zero read-ing Aon. the two;phasesindicatorsg"maands 'llzwhenftherreferenceioscillator weiss-connecteur l to theamplier inputs.- Whenever at subsequent times the switches 311-36 are turned to the alternate positions the phase indicators 'lil and 'il should read zero and any deviation from this standard reference reading constitutes an indication that some part of the apparatus requires adjustment.

The reference oscillator 79 is also made of the adjustable frequency type so that in the event the amplier tuning is changed as described in the preceding paragraphs to other frequencies, such as 88, 66 and 99 kilocycles, the oscillator frequency may be similarly changed to 11 kilocycles to permit a check on the operation of the vsystem to be made at the new frequency.

In the foregoing description, reference has been :made to the reference oscillator l and the harmonic generator e'l as operating at a relatively low frequency fundamental and capable of producing an output rich in the higher harmonics. Any suitable oscillator or harmonic generator having these properties may be employed. However, I prefer to use a signal generator of the type disclosed in my copending application Serial No. 612,988, filed August 27, 1945, now Patent No. 2,524,677 issued October 3, 1950, and entitled Signal Generator.

The phase discriminators 64 and 'i3 and the phase indicators 'I9 and 1l also may be of any suitable type, but a preference is expressed forthe types shown respectively in my copending applications Serial No. 612,991, led August 27, 1945, and entitledmMultiple Channel Radio Frequency Receiver, and Serial No. 612,984, filed August 27 1945, and entitled Registering Goniometer.

Attention is directed to the fact that with the embodiment of my invention which has been dea scribed in the immediately foregoing paragraphs, the tuning of the apparatus may be changedw as desired to permit one group of navigational system transmitters to be selected out of a plurality of such groups which may be arranged as a chain or network of navigational systems to cover extremely large areas. It will be noted that the principal amplifying function of the receiving apparatus is done in the heterodyne frequency amplifiers, and that these amplifiers may be of the fixed frequency type permitting high gain to be realised and permitting great phase stability to be readily obtained and easily maintained.

Attention is also directed to the fact that in both of the modifications of my invention which have been described herein the phase comparison is made at frequencies equal to or lower than. the lowest frequency transmitted by the navi-- gational system transmitters and that regardless of the frequency at which the phase comparison is made, the phaserelation which is indicated by the phase indicators is that which corresponds to a phase measurement made at a frequency equal to the lowest common multiple of the unlike frequencies whose multiple phase relation is to be determined. f

While I have shown and described the preferred embodiment of my invention I do not desire to be limited to the details of construction shown and described herein, except as dened in the appended claims.

I claim:

1. In a receiving apparatus for use with a radio frequency navigational system operating to transmit from spaced points a pair of radio frequency signals of unlike but related frequencies bearing a fixed multiple phase relation to each other, the` combination of: a pair of radio frequency re- Sii) ceivers tuned respectively to the frequencies of' said signals; means for combining and rectifying the combined outputs of said receivers to produce a heterodyne frequency equal to the difference between said frequencies; frequency multiplying means for converting said heterodyne frequency to equality with one of said signal frequencies; and means for measuring and indicating the phase relation between said converted frequency and said one frequency.

2. In a receiving apparatus for use with a radio frequency navigational system operating to transmit from spaced points a pair of radio frequency signals of unlike but related frequencies bearing a fixed multiple phase relation to each other, the combination of: a pair of radio frequency receivers tuned respectively to the frequencies of said signals; means for combining and rectifying the combined outputs of said receivers to produce a heterodyne frequency equal to the difference between said frequencies; frequency multiplying means for converting said heterodyne frequency to equality with the lowest one of said signal frequencies; and means for measuring and indicating the phase relation between said converted frequency and said lowest frequency.

3. The method of determining the multiple phase relation between two radio frequency signals of unlike but related frequencies which includes the steps of deriving a beat note equal in frequency to the difference between said two frequencies, converting the frequency of said beat note to equality with one of said frequencies, and measuring the phase relation between said one frequency and said converted frequency.

4. The method of determining the multiple phase relation between two radio frequency signals of unlike but related frequencies which consists in receiving, mixing and rectifying said signals to produce an output frequency equal to the difference between said two frequencies, multiplying said output frequency to a converted frequency equal to the frequency of one of said two signals, measuring the phase relation between u said converted frequency and said one signal, and

continuously indicating the result of said measurement. Y

5. In a receiving apparatus for use with a radio frequency navigation system operating to trans- Init from spaced points a pair of radio frequency signals of unlike but related frequencies bearing a fixed multiple phase relation to each other, the combination of: means for receiving both of said signals and producing an output potential having a frequency equal to the difference between said signal frequencies; means for converting the frequency of said output potential to equality with one of said signals; and means for measuring the phase relation between said converted output potential and said one of said signals.

WILLIAM J. OBRIEN.

' nie of this patent:

UNITED STATES PATENTS Number Name Date 2,144,203 Shanklin Jan. 17, 1939 2,252,699 Byrne Aug. 19, 1941. 2,408,773 Goodall Oct. 8, 1946 Y FOREIGN PATENTS Number Country Date y 547,183 -Great Britain Aug. 17, 1942 

